Gateless switch with capacitively-coupled contacts

ABSTRACT

A switch includes an input contact and an output contact to a conducting channel. At least one of the input and output contacts is capacitively coupled to the conducting channel. A control contact is located outside of a region between the input and output contacts, and can be used to adjust the switch between on and off operating states. The switch can be implemented as a radio frequency switch in a circuit.

REFERENCE TO PRIOR APPLICATIONS

The current application is a continuation of U.S. application Ser. No.12/651,470, which was filed on 3 Jan. 2010, which issued on 19 Nov. 2013as U.S. Pat. No. 8,587,028, and which claims the benefit of U.S.Provisional Application No. 61/204,368, titled “Gateless radio-frequencyswitch with capacitively-coupled contacts,” which was filed on 6 Jan.2009, both of which are hereby incorporated by reference.

GOVERNMENT LICENSE RIGHTS

The U.S. Government has a paid-up license in this invention and theright in limited circumstances to require the patent owner to licenseothers on reasonable terms as provided for by the terms of contract no.FA8650-09-C7931 awarded by the United States Air Force (USAF)/Air ForceMaterial Command (AFMC).

TECHNICAL FIELD

The disclosure relates generally to switches, and more particularly, toa gateless switch with capacitively-coupled contacts.

BACKGROUND ART

Solid state radio frequency (RF) switches are important components ofRadar transmit/receive (T/R) modules, satellite communication systems,Joint Tactical Radio Systems (JTRS), and the like. A promising RF switchtechnology uses Heterostructure Field Effect Transistors (HFETs).Recently, high power switches made of AlGaN/GaN HFETs demonstratedsuperior performance over other RF switching devices in terms of maximumpower density, bandwidth, operating temperature, and breakdown voltage.

Many applications, including JTRS and low-noise receivers, require RFswitches with a very low insertion loss, e.g., typically below 0.3decibels (dB). A low loss switch dissipates little RF power. As aresult, it can be fabricated over a low cost substrate, such assapphire. Low insertion loss in an HFET is due to a high channelconductance of the device, which is proportional to a total length ofthe device periphery. Exceptionally high 2D electron gas densities atthe AlGaN/GaN interface make a group III-Nitride HFET with a totalperiphery of two to five mm an ideal candidate for RF switchingapplications.

The feasibility of high-power broad-band monolithically integrated groupIII-Nitride HFET RF switches has been demonstrated. Large signalanalysis and experimental data for a large periphery group III-Nitrideswitch indicate that the switch can achieve switching powers exceeding+40 to +50 dBm.

Quality ohmic contact formation is a significant problem in themanufacture of wide band gap semiconductor devices. In particular, hightemperature annealing (e.g., at 850-900 degrees Celsius) leads tomaterial degradation during post-growth processing in the manufacturingprocess. For operating frequencies in the gigahertz range, groupIII-Nitride-based RF switches can be manufactured usingcapacitively-coupled contacts. The manufacture of suchcapacitively-coupled contacts can be performed using a self-alignedmetallization process that does not require contact annealing. Thisprocess provides a reduction in material degradation and simultaneousformation of RF input, output and control electrodes. RF switches withcapacitively-coupled contacts can be manufactured using either Schottkyelectrodes deposited over a wide band gap barrier layer ormetal-oxide-semiconductor (MOS) structures with electrodes formed overoxide-semiconductor heterojunction films.

The resulting RF switch with capacitively-coupled contacts can comprisea very low contact resistance at RF frequencies, particularlyfrequencies of approximately two gigahertz and above. Additionally, suchgroup III-Nitride switches have been shown to be capable of low-losshigh power RF switching. For example, a group-III Nitride RF switch withcapacitively-coupled contacts has provided insertion loss below onedecibel with isolation of thirty decibels in the frequency range of oneto eleven gigahertz.

SUMMARY OF THE INVENTION

Aspects of the invention provide a switch, which includes an inputcontact and an output contact to a conducting channel. At least one ofthe input and output contacts is capacitively coupled to the conductingchannel. A control contact is located outside of a region between theinput and output contacts, and can be used to adjust the switch betweenon and off operating states. The switch can be implemented as a radiofrequency switch in a circuit.

A first aspect of the invention provides a switch comprising: aconducting channel; an input contact to the conducting channel; anoutput contact to the conducting channel, wherein the input contact andthe output contact form opposing sides of an input-output region, andwherein at least one of the input contact or the output contact iscapacitively coupled to the conducting channel; and at least one controlcontact located outside of the input-output region.

A second aspect of the invention provides a circuit comprising: a radiofrequency (RF) switch including: a conducting channel; an input contactto the conducting channel; an output contact to the conducting channel,wherein the input contact and the output contact form opposing sides ofan input-output region, and wherein at least one of the input contact orthe output contact is capacitively coupled to the conducting channel;and at least one control contact located outside of the input-outputregion; a RF source electrically connected to the input contact; a RFoutput electrically connected to the output contact; and a RF controlcircuit electrically connected to the at least one control contact.

A third aspect of the invention provides a switch comprising: a barrierlayer comprising a wide band gap; and a buffer layer comprising a bandgap narrower than the barrier layer, wherein a conducting channel isformed at an interface of the barrier layer and the buffer layer; aninput contact to the conducting channel; an output contact to theconducting channel, wherein the input contact and the output contactform opposing sides of an input-output region, wherein the input contactand the output contact are located over the barrier layer, and whereinthe input contact and the output contact are capacitively coupled to theconducting channel; and at least one control contact located outside ofthe input-output region.

Other aspects of the invention provide circuits, devices, and methods ofdesigning, using and generating each, which include and/or utilize someor all of the switches and circuits described herein. The illustrativeaspects of the invention are designed to solve one or more of theproblems herein described and/or one or more other problems notdiscussed.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of the disclosure will be more readilyunderstood from the following detailed description of the variousaspects of the invention taken in conjunction with the accompanyingdrawings that depict various aspects of the invention.

FIG. 1 shows an illustrative gateless switch and an illustrative circuitincluding the switch according to an embodiment.

FIG. 2 shows a cross section of an illustrative switch with a controlcontact located on an opposing side of the conducting channel from theinput and output contacts according to an embodiment.

FIGS. 3A and 3B show a cross section of an illustrative switch in the onstate and off state, respectively, according to an embodiment.

FIGS. 4A and 4B show a cross section of another illustrative switch inthe on state and off state, respectively, according to an embodiment.

FIG. 5 shows an illustrative switch implemented using a heterostructureswitch technology according to an embodiment.

FIGS. 6A and 6B show illustrative switches including one or more lowconducting layers between the contacts according to embodiments.

FIG. 7 shows RF transmission of an illustrative switch manufacturedusing capacitively coupled contacts for the input contact, outputcontact, and both control contacts according to an embodiment.

It is noted that the drawings may not be to scale. The drawings areintended to depict only typical aspects of the invention, and thereforeshould not be considered as limiting the scope of the invention. In thedrawings, like numbering represents like elements between the drawings.

DETAILED DESCRIPTION OF THE INVENTION

As indicated above, aspects of the invention provide a switch, whichincludes an input contact and an output contact to a conducting channel.At least one of the input and output contacts is capacitively coupled tothe conducting channel. A control contact is located outside of a regionbetween the input and output contacts, and can be used to adjust theswitch between on and off operating states. The switch can beimplemented as a radio frequency (RF) switch in a circuit. The absenceof the control contact in the RF input-RF output spacing can simplifyfabrication of the switch, increase an operating voltage for the switch,and/or reduce an off state device capacitance. It is understood that forthe purposes of the present invention, Al means Aluminum, As meansArsenic, C means Carbon, In means Indium, Ga means Gallium, Hf meansHafnium, N means Nitrogen, O means Oxygen, P means Phosphorous, and Simeans Silicon. As used herein, unless otherwise noted, the term “set”means one or more (i.e., at least one) and the phrase “any solution”means any now known or later developed solution.

Turning to the drawings, FIG. 1 shows an illustrative gateless switch 10according to an embodiment. As illustrated, switch 10 includes asubstrate 12 on which a conducting channel 14 is located. Substrate 12can comprise any type of substrate, such as sapphire, substratematerials with a low dielectric permittivity, or the like.

As described further herein, channel 14 can be formed using any type ofelementary or compound semiconductor material system. In an embodiment,channel 14 comprises a heterostructure channel formed at an interface ofa barrier layer comprising a wide band gap and a buffer layer comprisinga band gap that is narrower than the band gap of the barrier layer. Forexample, channel 14 can be formed using compound semiconductorheterostructures including two or more layers of materials selected fromthe group-III nitride material system (e.g., Al_(X)In_(Y)Ga_(1-X-Y)N,where 0≦X, Y≦1, and X+Y≦1 and/or alloys thereof), two or more layers ofmaterials selected from the group-III arsenide material system (e.g.,Al_(X)Ga_(1-X)As, where 0≦X≦1, and/or alloys thereof), two or morelayers of materials selected from the InGaP material system (e.g.,In_(X)Ga_(1-X)P, where 0≦X≦1, and/or alloys thereof), and/or the like.Additionally, the channel 14 can be formed by n- or p-doped layers ofsilicon, germanium, or any other type of semiconductor materials.

Switch 10 further includes an input contact 20 and an output contact 22.Each contact 20, 22 can comprise a layer of metal, such as for example,titanium, aluminum, nickel, gold, and/or the like. One or both contacts20, 22 can comprise a capacitively coupled contact, which comprises ametal contact 20, 22 capacitively coupled to the conducting channel 14.To this extent, an insulating layer can be located between the metallayer of the contact 20, 22 and the channel 14. The insulating layer cancomprise any type of insulating material, such as a dielectric. Forexample, the insulating material can include oxygen containingdielectric materials (e.g., SiO₂, HfO₂, or the like), nitrogencontaining dielectric materials, such as a SiN compound (e.g., SiN,Si₃N₄), and/or the like. In an embodiment, a capacitively coupledcontact 20, 22 comprises a multi-layered contact, which includes aninsulating layer located over the conducting channel 14 and a metallayer located over the insulating layer. However, an insulating layercan be formed using any solution. For example, a semiconductor materialon which contacts 20, 22 are formed can include a depletion region overwhich the contacts 20, 22 are located. Alternatively, a highly resistivesemiconductor material can form the insulating layer. Furthermore, theinsulating layer can be formed by an air gap between the contacts 20, 22and the semiconductor structure including channel 14.

Switch 10 also includes at least one control contact, such as controlcontacts 24A, 24B. Each control contact 24A, 24B is located outside ofan input-output region 26 defined by adjacent sides of contacts 20, 22,making switch 10 a gateless switch. A control contact 24A, 24B cancomprise any type of contact having a strong coupling (ohmic orcapacitive) with the conducting channel 14. To this extent, anillustrative control contact 24A, 24B can comprise a capacitivelycoupled contact to the channel 14, which can be configured similar tocontacts 20, 22 as shown and described herein. Alternatively, anillustrative control contact 24A, 24B can comprise an ohmic contact tothe channel 14. The ohmic contact can comprise a metal layer (e.g.,titanium, aluminum, nickel, gold, and/or the like). In an embodiment,the ohmic contact further includes a contact layer on which the metallayer is formed. The contact layer can comprise at least Al and In. Forexample, the contact layer can comprise a p-type semiconductor andsubstantially consists of Al, In, Ga, and N.

In an embodiment, switch 10 operates as a radio frequency (RF) switch inwhich input contact 20 is a RF input contact and output contact 22 is aRF output contact in an integrated high power semiconductor devicecircuit 30. Circuit 30 can be implemented as part of a semiconductordevice configured to implement any type of application, including butnot limited to, a radar, a detector, a power amplifier, a rectifier, awireless communication unit, any type of power converter, and/or thelike.

Circuit 30 is shown including a RF input circuit 32, which generates aRF signal and transmits the RF signal to input contact 20. When switch10 is operating in the on state, the RF signal is transmitted from inputcontact 20 to output contact 22 via conducting channel 14, and isfurther transmitted to a RF output circuit 34 included in circuit 30. Inan embodiment, input contact 20 is monolithically integrated with aninput transmission line from RF input circuit 32, and output contact 22is monolithically integrated with an output transmission line to RFoutput circuit 34. Control circuit 36 is electrically connected to oneor more of the control contact(s) 24A, 24B and is configured to turnswitch 10 on and off using the control contacts(s) 24A, 24B.

In an embodiment, control circuit 36 modulates the operating state ofswitch 10, and the transmission between contacts 20, 22,electro-statically. To this extent, control circuit 36 can apply avoltage bias to one or both control contacts 24A, 24B, which modulates adepletion region under one or both contacts 20, 22. As a result, aninput-output impedance for switch 10 is also adjusted.

While switch 10 is shown including two control contacts 24A, 24B locatedon a surface of switch 10 adjacent to contacts 20, 22, respectively, itis understood that control contact(s) 24A, 24B can be located anywhereon switch 10 outside of region 26. For example, control contact(s) 24A,24B can be located on an opposing side of channel 14 from contacts 20,22. To this extent, FIG. 2 shows a cross section of an illustrativeswitch 10A with a control contact 24 located on an opposing side of theconducting channel 14 from the input contact 20 and output contact 22according to an embodiment. As illustrated, a single control contact 24can be located below substrate 12. In another embodiment, substrate 12can comprise a conducting substrate, such as SiC, GaN, and/or the like,which can be configured to function as a control contact as describedherein.

FIGS. 3A and 3B show a cross section of an illustrative switch 10B inthe on state and off state, respectively, according to an embodiment.Switch 10B is implemented with capacitively coupled control contacts24A, 24B. The dashed areas under the contacts 20, 22, 24A, 24B indicatedepletion regions. The length and the width of the depletion regionsunder the input contact 20 and output contact 22 increase as a reversebias voltage between the contacts 20, 22 and the channel 14 increases.The bias voltage (electrical potential difference) is supplied bycontrol contacts 24A, 24B located outside the input-output region 26(FIG. 1).

In the on state shown in FIG. 3A, control contacts 24A, 24B can supply azero or forward voltage bias between the control contacts 24A, 24B andcontacts 20, 22, which generates the corresponding depletion regionsunder the respective contacts 20, 22, 24A, 24B. In particular, a reversebias voltage can be applied to control contacts 24A, 24B. In this case,the depletion regions under control contacts 24A, 24B extend such thatthe channel 14 disappears under control contacts 24A, 24B. However,contacts 20, 22 are forward biased. As a result, the depletion regionsunder contacts 20, 22, are relatively small, allowing the signal to passfrom input contact 20 to output contact 22.

In the off state shown in FIG. 3B, a forward bias voltage applied to thecontrol contacts 24A, 24B reverse-biases the contacts 20, 22 beyond thepinch-off voltage of the portions of the channel 14 under contacts 20,22. In particular, since contacts 20, 22 are capacitively coupled tochannel 14, the reverse voltage bias applied between the input contact20 and the channel 14 and between the output contact 22 and the channel14 generates a depletion region under each of the contacts 20, 22. Asthe depletion region extends such that the conducting channel 14 underthe contact 20, 22 disappears as shown in FIG. 3B, the switch 10B entersa pinched-off mode and the conductance between the contacts 20, 22becomes very small.

FIGS. 4A and 4B show a cross section of another illustrative switch 100in the on state and off state, respectively, according to an embodiment.Switch 100 is implemented with ohmic control contacts 24A, 24B. Thedashed areas under the contacts 20, 22 indicate depletion regions.Similar to operation of switch 10B shown in FIGS. 3A, 3B, the length andthe width of the depletion regions under the input contact 20 and outputcontact 22 increase as a reverse bias voltage between the contacts 20,22 and the channel 14 increases. The bias voltage is supplied by controlcontacts 24A, 24B located outside the input-output region 26 (FIG. 1).

The required voltage bias between contacts 20, 22 and channel 14 to turnthe switch off can vary based on the materials used to fabricatecontacts 20, 22 and channel 14. For example, for a typicalheterostructure channel 14 formed by a group III-nitride material, avoltage bias between approximately 3-8 volts may be required, while atypical heterostructure channel 14 formed by a AlGaAs- or InP-basedmaterial may require a voltage bias between approximately 1-3 volts. Toobtain the necessary voltage bias using the capacitive control contacts24A, 24B shown and described with reference to FIGS. 3A and 3B, avoltage bias up to approximately twice the required voltage bias to turnthe switch off may need to be applied to control contacts 24A, 24B dueto additional voltage across the control contacts 24A, 24B capacitance.However, the ohmic control contacts 24A, 24B shown and described withreference to FIGS. 4A and 4B can require a bias voltage approximatelythe same as the voltage bias required to turn the switch off.

As discussed herein, the illustrative switches shown and describedherein can be manufactured using any of various material systems andtechnologies. To this extent, FIG. 5 shows an illustrative switch 10Dimplemented using a heterostructure switch technology according to anembodiment. Switch 10D comprises a heterostructure 11 that includes asubstrate 12 on which a buffer layer 16 is located. Further, theheterostructure 11 includes a barrier layer 18 located on the bufferlayer 16. A heterostructure channel 14 is formed at an interface of thebarrier layer 18 and the buffer layer 16. To this extent, the barrierlayer 18 comprises a wide band gap and the buffer layer 16 comprises aband gap that is narrower than the barrier layer 18. Substrate 12 cancomprise any type of substrate, such as sapphire, highly resistivesilicon, gallium arsenide, SiC, other semiconductor materials,dielectric materials (e.g., diamond), or the like. Buffer layer 16 canbe formed using GaN and barrier layer 18 can be formed using AlGaN.Alternatively, buffer layer 16 can be formed using GaAs and barrierlayer 18 can be formed using AlGaAs.

Additionally, heterostructure 11 can include an insulating layer 19located on the barrier layer 18 thereby forming aninsulator/semiconductor compound heterostructure. Insulating layer 19can comprise any type of insulating material, such as a dielectric. Tothis extent, the insulating material can comprise, for example, oxygencontaining dielectric materials (e.g., SiO₂, HfO₂, or the like).Insulating layer 19 can decrease a capacitance of switch 10D and anamount of leakage current during operation of switch 10D. Further,insulating layer 19 can enable switch 10D to be operated at highervoltages. Additionally, when insulating layer 19 is included, thecapacitively coupled contact(s) can comprise only a metal layer.

It is understood that heterostructure 11 is only illustrative of variousheterostructures that can be utilized to manufacture a switch. Forexample, heterostructure 11 can comprise an inverted heterostructure, ametal-semiconductor heterostructure, a doped channel metal-semiconductorheterostructure, a metal oxide semiconductor heterostructure, a metalinsulator semiconductor heterostructure, a doped channelmetal-insulator-semiconductor heterostructure, a double heterostructure,and/or the like.

In an illustrative embodiment, the switch described herein is configuredto provide a lower channel resistance, which can enable the switch toachieve lower loss, higher isolation, or both depending on a layout of acircuit in which the switch is implemented. For example, the switch caninclude more than one conducting channel 14. The conducting channels 14can be formed by a heterostructure. To this extent, the heterostructurecan comprise a double heterostructure channel formed inside a quantumwell of narrower band gap materials placed between wide band gap barrierlayers. Further, the channel(s) of an embodiment of the switch describedherein can be doped with impurities, thereby increasing an equilibriumcarrier concentration in the channel 14, e.g., donors for a n-typechannel or acceptors for a p-type channel.

Embodiments of the switch shown and described herein can include one ormore additional layers. For example, FIGS. 6A and 6B show illustrativeswitches 10E, 10F, respectively, including one or more low conductinglayers between the contacts according to embodiments. The low conductinglayer(s) can be formed using a material such as a semiconductor, adielectric, a polymer, a liquid, and/or the like. In FIG. 6A, switch 10Eincludes a low-conducting layer 40 located in the input-output region 26(FIG. 1). Low-conducting layer 40 can be formed (e.g., deposited) on thesurface of the switch 10E between input contact 20 and output contact22. Low-conducting layer 40 can make electrical contact with bothcontacts 20, 22.

The steady-state potential at low-conducting layer 40 is the same asthat at the contacts 20, 22. Therefore, if the portions of the channel14 under the contacts 20, 22 are in the pinch-off condition, so is theportion of the channel 14 under the low-conducting layer 40. As aresult, the entire channel 14 in the RF input-RF output spacing isdepleted resulting in very low input-output capacitance. When thecontacts 20, 22 are at zero or positive potential, the entire channel 14in the RF input-RF output spacing is un-depleted.

In FIG. 6B, switch 10F includes three low-conducting layers 42A-42C.Low-conducting layer 42A is located between control contact 24A andinput contact 20, low-conducting layer 42B is located between inputcontact 20 and output contact 22, and low-conducting layer 42C islocated between output contact 22 and control contact 24B. Eachconducting layer 42A-42C can make electrical contact with both of thecorresponding adjacent contacts. In addition to depleting the entirechannel 14, low-conducting layers 42A-42C also can reduce thecapacitance between the contacts 20, 22 and the control contacts 24A,24B.

FIG. 7 shows RF transmission of an illustrative switch manufacturedusing the capacitively coupled contacts for the input contact, outputcontact, and both control contacts according to an embodiment. Asillustrated, at a zero or negative voltage bias at the control contacts,the switch is in the on state. At a negative voltage bias at the inputand output contacts (a positive bias at the control contacts), theswitch is in the off state. In the off state, the conducting channelbetween the input and output contacts disappears, and the RF couplingbetween the input and output contacts is only provided by small edgecapacitances of the contacts to the channel between the contacts (e.g.,below input-output spacing 26 of FIG. 1). When a low-conducting layer isincluded between the input and output contacts, the capacitance furtherreduces down to a geometrical capacitance between the two metalelectrodes (typically less than 0.1 picofarad/millimeter (pF/mm).

While primarily shown and described herein as a switch and acorresponding circuit, it is understood that aspects of the inventionfurther provide various alternative embodiments. In one embodiment, theinvention provides a method of fabricating (manufacturing) a switchdescribed herein. For example, a structure capable of forming one ormore conducting channels, such as a heterostructure 11 (FIG. 5), can beobtained using any solution. The structure can be purchased or otherwiseacquired, fabricated (e.g., by growing or depositing layer(s) in theheterostructure), or the like. The various contacts 20, 22, 24A, 24B canbe formed on a surface of the structure. For example, a metal for eachcontact 20, 22, 24A, 24B can be deposited and/or shaped using anysolution. By forming contacts 24A, 24B outside of the input-outputregion 26, fabrication of the switch is simplified.

In another embodiment, the invention provides a method of fabricating acircuit, such as circuit 30 of FIG. 1, including the switch describedherein. For example, input contact 20 can be electrically connected to aconductor (e.g., transmission line) carrying an RF signal from a RFinput circuit 32, and output contact 22 can be electrically connected toa conductor carrying the RF signal to a RF output circuit 34. In anembodiment, the electrical connections are made by monolithicallyintegrating the contacts 20, 22 with the conductors. Further, controlcontacts 24A, 24B can be electrically connected to a control circuit 36,which generates a control signal for switching the operating state ofthe switch 10 between on and off states.

In still another embodiment, the invention provides a method ofoperating a device including the RF switch 10. In particular, the methodincludes selectively enabling a RF signal to pass from a RF inputcircuit 32 to a RF output circuit 34 electro-statically, e.g., bymodulating depletion regions under an input contact 20 and an outputcontact 22, which adjusts an impedance for the switch. For example, theswitch can be transitioned between on and off operating states byapplying a bias voltage to control contact(s) 24A, 24B located outsideof the input-output region 26.

The foregoing description of various aspects of the invention has beenpresented for purposes of illustration and description. It is notintended to be exhaustive or to limit the invention to the precise formdisclosed, and obviously, many modifications and variations arepossible. Such modifications and variations that may be apparent to anindividual in the art are included within the scope of the invention asdefined by the accompanying claims.

What is claimed is:
 1. A switch comprising: a semiconductor structureincluding a conducting channel; an input contact to the conductingchannel located on a surface of the semiconductor structure; an outputcontact to the conducting channel located on the surface of thesemiconductor structure, wherein the input contact and the outputcontact form opposing sides of an input-output region, wherein theinput-output region is further defined by the conducting channel and asurface of the semiconductor structure between the input and outputcontacts, and wherein at least one of the input contact or the outputcontact is capacitively coupled to the conducting channel; and at leastone control contact located outside of the input-output region, whereinthe at least one control contact is not located between the input andoutput contacts.
 2. The switch of claim 1, wherein the at least onecontrol contact is located on the surface of the semiconductor structureand is capacitively coupled to the conducting channel.
 3. The switch ofclaim 1, wherein the at least one control contact is an ohmic contact tothe conducting channel.
 4. The switch of claim 1, wherein the at leastone control contact includes a first control contact located adjacent tothe input contact and a second control contact located adjacent to theoutput contact.
 5. The switch of claim 1, wherein the at least onecontrol contact is located on an opposing side of the conducting channelfrom the input contact and the output contact.
 6. The switch of claim 5,wherein the at least one control contact comprises a conductingsubstrate.
 7. The switch of claim 1, the semiconductor structure furthercomprising: a barrier layer comprising a wide band gap, wherein theinput contact and the output contact are located over the barrier layer;and a buffer layer comprising a band gap narrower than the barrierlayer, wherein the conducting channel is formed at an interface of thebarrier layer and the buffer layer.
 8. The switch of claim 7, thesemiconductor structure further comprising an insulating layer locatedover the barrier layer, wherein the input contact and the output contactare located over the insulating layer.
 9. The switch of claim 1, thesemiconductor structure further comprising an insulating layer locatedin the input-output region, wherein the insulating layer contacts theinput contact and the output contact.
 10. The switch of claim 9, thesemiconductor structure further comprising a second insulating layerlocated between the input contact and one of the at least one controlcontact and a third insulating layer located between the output contactand another one of the at least one control contact.
 11. The switch ofclaim 1, the semiconductor structure further comprising a secondconducting channel, wherein the input contact, the output contact andthe at least one control contact are coupled to the second conductingchannel, and wherein at least one of the input contact or the outputcontact is capacitively coupled to the second conducting channel. 12.The switch of claim 1, wherein the conducting channel is doped withimpurities.
 13. A circuit comprising: a radio frequency (RF) switchincluding: a semiconductor structure including a conducting channel; aninput contact to the conducting channel located on a surface of thesemiconductor structure; an output contact to the conducting channellocated on the surface of the semiconductor structure, wherein the inputcontact and the output contact form opposing sides of an input-outputregion, wherein the input-output region is further defined by theconducting channel and a surface of the semiconductor structure betweenthe input and output contacts, and wherein at least one of the inputcontact or the output contact is capacitively coupled to the conductingchannel; and at least one control contact located outside of theinput-output region, wherein the at least one control contact is notlocated between the input and output contacts; a RF source electricallyconnected to the input contact; a RF output electrically connected tothe output contact; and a RF control circuit electrically connected tothe at least one control contact.
 14. The circuit of claim 13, whereinthe RF control circuit is configured to turn the RF switch off bygenerating a reverse voltage bias at the input and output contacts withrespect to the conducting channel using the at least one controlcontact.
 15. The circuit of claim 13, wherein the RF control circuit isconfigured to turn the RF switch on by generating one of: a zero voltageor a forward voltage bias at the input and output contacts with respectto the conducting channel using the at least one control contact. 16.The circuit of claim 13, wherein the input contact is monolithicallyintegrated with the RF input and the output contact is monolithicallyintegrated with the RF output.
 17. The circuit of claim 13, wherein thesemiconductor structure further includes an insulating layer located inthe input-output region, wherein the insulating layer contacts the inputcontact and the output contact.
 18. A switch comprising: a semiconductorstructure including: a barrier layer comprising a wide band gap; and abuffer layer comprising a band gap narrower than the barrier layer,wherein a conducting channel is formed at an interface of the barrierlayer and the buffer layer; an input contact to the conducting channellocated over the barrier layer on a surface of the semiconductorstructure; an output contact to the conducting channel located over thebarrier layer on the surface of the semiconductor structure, wherein theinput contact and the output contact form opposing sides of aninput-output region, wherein the input-output region is further definedby the conducting channel and a surface of the semiconductor structurebetween the input and output contacts, and wherein the input contact andthe output contact are capacitively coupled to the conducting channel;and at least one control contact located over the barrier layer outsideof the input-output region, wherein the at least one control contact isnot located between the input and output contacts.
 19. The switch ofclaim 18, the semiconductor structure further comprising an insulatinglayer located over the barrier layer, wherein the input contact and theoutput contact are located over the insulating layer.
 20. The switch ofclaim 18, the semiconductor structure further comprising an insulatinglayer located in the input-output region, wherein the insulating layercontacts the input contact and the output contact.